Indi, IN What has to happen in Episode III

This isn't really relevant to Ep3, but as I was watching ANH today, I noticed (speaking of bad SFX) that when Obi-1 and Vader are dueling, there is a point at which Obi's blade (the prop itself) BENDS to the left due to pressure from Vader's prop. Has anyone else ever noticed this? 'Cause I've seen the movie 16 times and I just noticed it!